1. Field of the Invention
The present invention relates to an apparatus that starts an internal combustion engine that is linked with a rotating shaft of a motor via a damper, a starting control method, and a starting control apparatus for a hybrid vehicle with an internal combustion engine and a motor mounted thereon.
2. Description of the Related Art
A typical structure to start an internal combustion engine mounted on a vehicle cranks the internal combustion engine with a self-starting motor, which is specifically used for starting and linked with a rotating shaft of the internal combustion engine, and simultaneously feeds a supply of fuel. The self-starting motor is a small-sized motor for starting the internal combustion engine and enables the internal combustion engine to be rotated only to a significantly lower revolving speed (several hundred rpm) than an idle speed. The internal combustion engine is driven to a certain level of revolving speed that enables subsequent self starting and driving, through combustion of the supplied fuel.
In a hybrid vehicle which has an internal combustion engine and a motor mounted thereon and outputs a power for driving at least from the motor, some proposed systems do not have a self-starting motor specifically used for starting but uses a motor that is linked with a rotating shaft of an internal combustion engine to start the internal combustion engine (for example, JAPANESE PATENT LAID-OPEN GAZETTE No. 6-144020 and No. 9-222064. In this system, the rotating shaft of the internal combustion engine is linked with a rotating shaft of a first motor via a first clutch, whereas the rotating shaft of the first motor is connected via a second clutch with a drive shaft that is mechanically linked with wheels. A second motor is further connected to the drive shaft. At the time of starting the internal combustion engine, while the first clutch is engaged and the second clutch is released, the first motor cranks or motors the internal combustion engine prior to a supply of fuel. When the revolving speed of the internal combustion engine becomes equal to or greater than a preset value, the supply of fuel is fed to the internal combustion engine, which subsequently starts through the compression and combustion of the air/fuel mixture. After the start of the internal combustion engine, the first motor is driven as a generator with the power output from the internal combustion engine to charge the battery or to output the power directly to the drive shaft and drive the vehicle while the second clutch is engaged.
In the conventional starting control apparatus for the hybrid vehicle, however, a large load is applied to the battery. The battery is exposed to an excessive load especially when the internal combustion engine has poor startability. This is ascribed to the following reasons:
(1) In the hybrid vehicle, the motor is larger in size than the conventional self-starting motor and consumes a greater amount of electric power;
(2) In the hybrid vehicle, the rotor of the motor, which has a significantly larger mass than that of the self-starting motor, is connected to the rotating shaft of the engine. This often causes torsional resonance. A large torque is output from the motor, in order to enable the revolving speed of the internal combustion engine to quickly pass through the range of possible torsional resonance. This increases the electric power consumed by the motor.
(3) In the hybrid vehicle, the motor can increase the revolving speed of the internal combustion engine to a higher level than that in the conventional vehicle. The supply of fuel to the internal combustion engine and the combustion of the air/fuel mixture accordingly start at the higher revolving speed, since the start of combustion at the higher revolving speed improves the emission. The increase in revolving speed of the internal combustion engine to the higher level, however, increases the amount of electric power consumed by the motor.
Among these problems, (2) and (3) are not negligible especially when the internal combustion engine is cold. When the internal combustion engine is cold, the high viscosity of lubricant causes the revolving speed of the internal combustion engine not to quickly increase, in response to supply of electric current to allow output of a large torque from the motor. A large electric power is accordingly consumed before the revolving speed reaches a preset level (for example, 800 rpm). The problems (1) through (3) are not only observed in the hybrid vehicle but in any other structures that use a large-sized self-starting motor.
One proposed countermeasure uniformly limits the supply of electricity from the battery according to the elapse of time (for example, JAPANESE PATENT LAID-OPEN GAZETTE No. 63-297767). This uniform limitation is, however, not practical, since a little more continuance of cranking may start the internal combustion engine. Especially in the case of the large-sized self-starting motor, one cranking operation consumes a large amount of electric power. Several tries of starting with limitation of the cranking time cause the battery to be exposed to a greater load.